Hobby and Interest

Hi! I would like to know what’s wrong with the following sentences:

A1. My interest is to reduce the threat of a nuclear war.
A2. My interest is to play basketball.
A3. My interest is playing basketball.
A4. My interest is basketball.
A5. My interest is the basketball.
A6. My interest is playing piano.
A7. My interest is playing the piano.

B1. I am interested in reducing the threat of a nuclear war.
B2. I am interested in playing basketball.
B3. My interest is in playing basketball.
B4. I am interested in basketball.
B5. I am interested in the basketball.
B6. I am interested in basketball games.
B7. I am interested in the basketball game.

C1. My hobby is to reduce the threat of a nuclear war.
C2. My hobby is to play basketball.
C3. My hobby is playng basketball.
C4. My hobby is basketball.

It really is unncessarily confusing, but even as I type, more confusions come to mind. Thanks in advance!
At first I thought that A2 is incorrect, but when I juxtapose it with A1, I am no longer sure. A1 must be correct because it is quoted from a native speaker of American English.

If “to do somthing” means that something has yet to be done, then does A2 mean that I wanted to play basketball but has been unable to do so? Does that mean that A2 is still correct but doesn’t mean what I want to mean?

If that is the case, does it mean that B1 is not the same as A1 in meaning?

Thanks for the reply, I am grateful.

Hobby and interest are usually placed together in the phrase “Hobbies and Interests” or in questions like “What are your hobbies or interests?”

What are the finer points of differences between them?

According to my dictionary, there is only one definition for “hobby”, “an activity that you enjoy doing in your free time”; while one of the 14 definitions for “interest” is “something you enjoy doing or a subject you enjoy studying when you are not working: Her main interest in life is tennis.” Yet the example given here seems to imply a lot more than leisure time activity.

As you yourself have already noticed, the word interest has a number of definitions and the varying definitions are also regularly used. It is always important to keep context in mind. ‘Reducing the threat of a nuclear war’ is not comparable to ‘playing basketball’ and that fact alone is a good indication that you need to apply a different definition to the word interest.

I would say that interest is synonymous with concern in your first sentence. It refers to a matter of importance.

Click here and look at definition number 4.